Light - yes quite literally the present and absence of light - is an environmental (biologically grounded) factor in health and happiness.

In a fairly rigorous study of 86772 adults, researchers “examined the independent association of day and night-time light exposure with covariate-adjusted risk for psychiatric disorders and self-harm. Greater night-time light exposure was associated with increased risk for major depressive disorder, generalized anxiety disorder, PTSD, psychosis, bipolar disorder, and self-harm behavior. Independent of night-time light exposure, greater daytime light exposure was associated with reduced risk for major depressive disorder, PTSD, psychosis, and self-harm behavior. These findings were robust to adjustment for sociodemographics, photoperiod, physical activity, sleep quality, and cardiometabolic health. Avoiding light at night and seeking light during the day may be a simple and effective, non-pharmacological means of broadly improving mental health.”

This relates to the 6 factors outlined here 3. Biological factors play a role in happiness.

Light exposure, particularly sunlight in the morning within 30 minutes of waking, also plays a critical role in regulating ultradian and circadian rhythms which govern a host of physiological processes influencing mental and physical health.